The present invention relates to a thermoplastic resin film having improved printability. More improved in ink transfer and adhesion that comprises a polyolefin film which has formed thereon a coating containing a specified compound.
The thermoplastic resin film, in particular, synthetic paper provided by the present invention is useful as the base paper of stickers for outdoor advertisement, labels on frozen food containers and namers on industrial products (i.e., labels describing their use and precautions that should be exercised).
Stickers for outdoor advertisement and labels to be attached to frozen food containers have conventionally been made of coated paper made of pulp fibre. However, coated paper is rather poor in water resistance and in order to compensate for this defect, attempts have recently been made to laminate its surface with polyester films. More recently, synthetic paper made of polyolefin having better resistance to water has gained increasing attention as a promising substitute for such coated paper. However, because of the non-polarity and hydrophobicity of the polyolefin from which it is made, such new synthetic paper is not completely satisfactory in terms of adaptability for offset printing and processability and is normally used after it has been given an appropriate surface treatment, for example, application of a coating agent to the surface of the paper. It is already known to use polyethylene-imine or an ethyleneimine/ethylene urea copolymer as such coating agent or anchor coating agent [see JP-B-40-12302, JP-B-53-6676 and JP-A-57-149363 (the terms "JP-A" and "JP-B" as used herein respectively mean an "unexamined published Japanese application" and an "examined Japanese patent publication")].
The method of surface treatment which uses polyethylene-imine as an anchor coating agent is capable of producing a film that has satisfactory printability for practical purposes if the film is a fresh one which has just been treated. However, if the resin film is stored either under hot conditions or for a period as long as one year before printing, insufficient ink transfer or ink adhesion that is too low to warrant practical use will sometimes take place during printing operations, in particular, those of printing with UV radiation curable ink (which is hereunder referred to as UV curable ink) or offset printing ink.